The present invention generally relates to dispensing systems for applying a liquid material and, more particularly, for dispensing a filament or filaments of liquid, such as hot melt adhesive, on a substrate.
Various liquid dispensing systems use air assisted extrusion nozzles to apply viscous material, such as thermoplastic material, onto a moving substrate. Often times, these systems are used to form nonwoven products. For example, meltblowing systems may be used during the manufacture of products such as diapers, feminine hygiene products and the like. In general, meltblowing systems include a source of liquid thermoplastic material, a source of pressurized process air, and a manifold for distributing the liquid material and process air. A plurality of modules or dispensing valves may be mounted to the manifold for receiving the liquid and process air and dispensing an elongated filament of the liquid material which is attenuated and drawn down by the air before being randomly applied onto the substrate. In general, a meltblowing die tip or nozzle includes a plurality of liquid discharge orifices arranged in a row and a slot on each side of the row of liquid discharge orifices for dispensing the air. Instead of slots, it is also well known to use two rows of air discharge orifices parallel to the row of liquid discharge orifices.
Controlled fiberization dispensing systems also use air assisted extrusion nozzles. However, the pressurized process air in these systems is used to swirl the extruded liquid filament. Conventional swirl nozzles or die tips typically have a central liquid discharge passage surrounded by a plurality of process air discharge passages. The liquid discharge passage is centrally located on a protrusion. A common configuration for the protrusion is conical or frustoconical with the liquid discharge passage opening at the apex. The process air discharge passages are typically disposed at the base of the protrusion. The process air discharge passages are usually arranged in a radially symmetric pattern about the central liquid discharge passage. The process air discharge passages are directed in a generally tangential manner relative to the liquid discharge orifice and are all angled in a clockwise or counterclockwise direction around the central liquid discharge passage.
Another type of air assisted nozzle, referred to herein as a bi-radial nozzle, includes a wedge-shaped member having a pair of side surfaces converging to an apex. A liquid discharge passage extends along an axis through the wedge-shaped member and through the apex. The wedge-shaped member extends in a radially asymmetrical manner around the liquid discharge passage. Four process air discharge passages are positioned at the base of the wedge-shaped member. At least one process air discharge passage is positioned adjacent to each of the side surfaces and each of the process air discharge passages is angled in a compound manner generally toward the liquid discharge passage and offset from the axis of the liquid discharge passage.
These and other types of air-assisted extrusion nozzles generally require periodic maintenance due to accumulation of dust, hardened liquid material, or other reasons. Each dispensing valve may have to be unbolted from the manifold by unscrewing at least two bolts. The nozzle is then removed from the dispensing valve and another nozzle is mounted onto the valve. If necessary, the valve is reattached to the manifold. Consequently, such repair can increase the required shut down time for removal and replacement of valves and nozzles. Removal of the entire dispensing valve with the attached nozzle is generally a requirement when changing between applications (e.g., meltblowing to controlled fiberization).
For these reasons, it is desirable to provide apparatus and methods for quickly changing nozzles on a die assembly without encountering various problems of prior liquid dispensing systems. It is also desirable to provide for easier maintenance and replacement of air-assisted extrusion nozzles.
Generally, the present invention provides an apparatus for dispensing a filament of liquid assisted by pressurized process air. The apparatus comprises a housing having a liquid supply passage, a process air supply passage, and a nozzle mounting surface which may be disposed within a recess of the housing. A nozzle includes an inlet side positioned adjacent the mounting surface and an outlet side having at least one liquid discharge orifice and a plurality of process air discharge passages adjacent the liquid discharge orifice. When properly mounted and aligned against the mounting surface, the liquid discharge orifice and the process air discharge air passages are respectively in fluid communication with the liquid supply passage and the process air supply passage of the housing. In one aspect of the invention, a nozzle ejecting lever is pivotally affixed to the housing and pivotally moves from a first position to a second position. In the first position, the nozzle may be mounted adjacent the mounting surface as described above and, as the ejecting lever is moved to the second position, the nozzle is pried away from the mounting surface. This assists in removing nozzles which may be otherwise adhered to the housing due to thermoplastic liquid or other reasons.
In another aspect of the invention, a nozzle positioning lever is pivotally affixed to the housing to move between first and second positions. In the first position the positioning lever allows the nozzle to be mounted in a sealing manner within the housing recess and adjacent the mounting surface. In the second position the positioning lever holds the nozzle in the recess with the process air discharge passages in fluid communication with the process air supply passage and with the liquid discharge orifice in fluid communication with the liquid supply passage. In the preferred embodiment, the positioning lever and the ejecting lever may be one and the same with different portions of the lever performing the position and ejecting functions.
In another aspect of the invention, a clamping lever is pivotally affixed to the housing and operates in conjunction with cam surfaces on the nozzle and the housing to clamp the nozzle within the housing recess. In the preferred embodiment, the positioning lever is used to first position the nozzle within the recess and temporarily hold the nozzle within the recess. The clamping lever is then used to fixedly secure the nozzle within the recess for the duration of the dispensing operation. For nozzle replacement, repair and other maintenance purposes, the clamping lever may be loosened and the positioning and ejecting lever may be used to pry the nozzle from the recess.
A plurality of nozzles are provided in a liquid dispensing system in accordance with the invention, with each nozzle configured to discharge a different filament pattern. For example, a first nozzle may be configured to dispense meltblown filaments while a second nozzle may be configured to dispense a swirl filament pattern. Each of the nozzles is constructed to be received in the recess such that the liquid discharge orifice or orifices of the nozzle and the process air discharge passages are respectively in fluid communication with the liquid supply passage and process air supply passage of the housing. Each nozzle is symmetrically configured such that the nozzle may be rotated 180xc2x0 and still be mountable within the housing recess. In this regard, the nozzle includes cam surfaces on opposite sidewall portions thereof which can each interchangeably engage the cam surface of the clamping lever or a cam surface formed on a wall of the recess.
Various advantages, objectives, and features of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings.